LIBERATION OF ORGANIC Matrer BY Roots oF Growinea Puants 35 
nd that these tests might possibly afford some information regarding 
he relation of the stage of growth of the plants to the presence of oxidizing 
r reducing substances. 
REVIEW OF LITERATURE 
Apparently the only examinations designed to detect the presence of 
educing substances in media in which plants grew were those conducted 
yy Schreiner and Sullivan (1910), who placed the roots, and in some 
ases the seeds also, of wheat seedlings in solutions of various reagents 
ommonly used for detecting the presence of reducing substances. Con- 
idering only the tests in which roots alone were introduced into the 
zagent solution, these authors obtained reactions with starch-iodide 
olution, sodium selenite, and sodium tellurite. Tests for reduction of 
itrates appear to have been made only where the seeds were present, 
nd under these conditions nitrites were found by means of the Griess 
saction. The seeds from which the seedlings were germinated had 
reviously been treated with a 0.1-per-cent solution of mercuric chloride. 
‘he solutions in which the plants grew were not shown to be sterile. 
It is well known that oxidizing enzymes occur within plant tissues 
nd they are believed to play an important part in physiological processes. 
‘hey have been found also in soils, but this does not furnish any proof 
iat they are liberated by plant roots altho it suggests such a possibility. 
‘he presence in soils of large numbers of bacteria many of which are 
nown to secrete enzymes, may well account for the appearance in soils 
' oxidizing enzymes without any contribution from roots of higher plants. 
; 1s equally true that the occurrence of enzymes within the plant would 
ot necessarily lead to the conclusion that they are thus conveyed to the 
il. 
Not many investigators have taken up studies concerning the liberation 
' oxidizing substances by plant roots. The work of Molisch, Czapek, 
aid Raciborski has been reviewed by Schreiner and Reed (1909), and 
ence it is not necessary to review it here. Schreiner and Reed, in the 
yper referred to, state that they have been able to detect the presence 
oxidizing enzymes on certain parts of the surface of wheat roots. For 
us purpose they used alpha-naphthylamine, benzidine, vanillin, vanillic 
id, phenolphthalin, aloin, and leuco-rosolic acid. As in their experiments 
r the detection of reducing substances, there was no evidence offered 
